286 LILY C. SHUDDEMAGEN. 



i. THE BRAIN. 



General Topography. 



The brain is almost twice as long as broad. The bulbus 

 olfactorius forms the most anterior, and the medulla oblongata 

 its most posterior parts. The cerebrum broadens out poster- 

 iori} 7 , and, on lateral view, is not quite as high as the cerebel- 

 lum. The general shape is much like that of the lower mammals. 



(a) Prosenceplialou. - - The prosencephalon is composed of the 

 following parts : bulbus olfactorius, tuberculum olfactorium, lobus 

 pyriformis, pedunculus olfactorius, locus perforatus, and the cere- 

 bral hemispheres. 



The bulbus olfactorius (PI. XXIV., Fig. i, Bui. Olf.} is the most 

 anterior part of the brain, and is relatively enormous. From a 

 ventral view, it is seen to be heartshaped with the apex pointing 

 forward. The ventral surface is indented by almost parallel fur- 

 rows or sulci, running at right angles to the long axis of the 

 brain. The dorsal surface (Fig. 4) is spherically rounded and 

 smooth. It is placed somewhat ventral to the cerebral hemi- 

 spheres (Fig. 2), so that over half of its dorsal surface is over- 

 lapped by them. From the anterior part of the bulbus olfactorius 

 the olfactory nerve spreads out in a great fan-shaped mass. 



The tuberculum olfactorium (PI. XXIV., Fig. i, Tub. Olf.} is a 

 large oval area slightly raised above the surrounding regions. 

 It is separated from the bulbus olfactorius by the pedunculus 

 olfactorius. Its surface is not smooth, but somewhat tubercu- 

 lated. It reaches a relatively large size in the armadillo. 



The lobus pyiifonnis is visible along the lateral surface of the 

 brain, just posterior to the tuberculum olfactorium ; it consists of 

 an anterior lobe (Lob. Pyr. A., Fig. 2), and a posterior (Lob. Pyr. 

 P., Fig. i). 



The pedunculus olfactorius (PI. XXIV., Fig. 3, Fed. Olf.} is 

 to be seen only in a lateral view of the brain. It connects the 

 bulbus olfactorius with the remainder of that organ. In both 

 dorsal (PI. XXIV., Fig. 4), and ventral (Fig. i), views it is hid- 

 den by the cerebral hemispheres and the oblique position of the 

 bulbus olfactorius. 



The locus perforatus (PI. XXIV., Fig. i, Loc. Perf.} is the 



